1. Field of the Invention
The present invention relates to an Automatic Repeat reQuest (ARQ) data recovery method, and more particularly, to an ARQ data recovery method for preventing data loss when handover is generated in a portable Internet system.
2. Description of the Related Art
A portable Internet system using a wireless transmission scheme for guaranteeing spectrum usage efficiency in a 2.3 GHz frequency bandwidth has a cellular-type network configuration, and it may efficiently use the uplink/downlink asymmetry transmission characteristics of an IP-based wireless service.
FIG. 1 shows a flow diagram of a handover process in a conventional portable Internet system;
As shown in FIG. 1, a mobile terminal 100 wirelessly accesses a base station to receive a service from a portable Internet network, and the base station that mobile terminal 100 accessed becomes a serving base station 210. Mobile terminal 100 measures a radio signal from serving base station 210 and neighboring base stations to reliably communicate with serving base station 210. In this case, when a quality of the radio signal received from serving base station 210 is lower than a quality of the radio signal received from a neighboring base station by a threshold value suggested in a handover algorithm realized in mobile terminal 100, mobile terminal 100 determines performing the handover to the neighboring base station.
Mobile terminal 100 uses a handover request HO-REQ message to request a handover from serving base station 210 in step S10. Serving base station 210 receiving the HO-REQ message requests the handover of mobile terminal 100 from an access router 300 in step S20, and access router 300 requests the handover from a neighboring base station having a radio signal threshold value that is greater than that of serving base station 210 in step S30.
The neighboring base station receiving the handover request in step S30 becomes a recommended target base station, and the recommended target base station transmits a response to the handover request to access router 300 in step S40. Access router 300 receiving the handover response transmits a response to the handover to serving base station 210 in step S50. Serving base station 210 receiving the handover response uses a handover response message HO-RSP to transmit information of the recommended target base station (i.e., a target base station 220) to mobile terminal 100 in step S60.
Mobile station 100 receiving a final handover notification transmits a handover indication message HO-IND to serving base station 210 in step S70. After the HO-IND message is transmitted to serving base station 210, serving base station 210 transmits a handover start message in step S80 to inform access router 300 that the handover is actually performed.
Access router 300 receiving the handover start message from serving base station 210 transmits the handover start message to target base station 220 in step S90. After receiving the handover start message from access router 300, target base station 220 transmits a response message of the handover start message to access router 300 in step S100 in response to the handover start message.
After receiving the response message of the handover start message from target base station 220, access router 300 changes the routing table in access router 300 and transmits the response message to serving base station 210 in step S110 so that transmissions to mobile terminal 100 are transmitted to target base station 220 rather than serving base station 210. Serving base station 210 receiving the response message transmits Automatic Repeat reQuest (ARQ) data or Service Data Unit (SDU) data to access router 300 in step S120 to transmit the ARQ or SDU data to selected target base station 220.
In the above conventional handover process, Internet Protocol (IP) packets, which are transmitted to serving base station 210 and are buffered to be transmitted to mobile terminal 100 but are not transmitted to mobile terminal 100, are transmitted to target base station 220 through access router 300 by using an IP routing function. However, when some ARQ blocks of all the ARQ blocks corresponding to one SDU are transmitted to mobile terminal 100, IP header information may be lost in the ARQ blocks. In that case, some IP packets may not be transmitted to the target base station by using the IP routing function, and a data loss may be problematically generated when the handover is performed.
When the SDU, which embodies the ARQ blocks, is stored in serving base station 210, the ARQ data may be recovered by transmitting information of the corresponding SDU and a sequence number of the ARQ blocks that has been transmitted without any error to target base station 220. However, in this case, since it is difficult to determine which part of the corresponding SDU corresponds to the sequence number of the transmitted ARQ block, it is required to reset the ARQ state in target base station 220 and mobile terminal 100 after the handover is performed, and the transmitted ARQ blocks may be transmitted again. Therefore, radio efficiency may be deteriorated, and the entire handover delay time is problematically increased.
The above information disclosed in this Background section is only for a better understanding of the background of the invention and therefore may contain information that is not prior art to a person of ordinary skill in the art.